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26
In his report on, rodent control work during 1957, Mr. Walker,
the senior public health inspector, states:—
"Notifications of infestation received were much the same as
in the previous year and were spread fairly evenly over the whole
borough. No infestation of a major character was discovered.
The sewer treatments were carried out during April and
September instead of June and December. Extended baiting was
carried out in September i.e. days 1, 3, 5 and 2, 4, 6 instead of consecutive
days, and this seems to have had the desired effect in that an
increased number of pre-bait takes were recorded. The poisons used
in these treatments were zinc phosphide and arsenious oxide, used
alternately. It has been recommended by the Ministry of Agriculture
that an experimental treatment with warfarin be carried out and it is
hoped that this can be done in the near future. Warfarin could not be
used previously as it has to be mixed with an oatmeal base which
deteriorates quickly in the humid atmosphere of the sewers, but a
mould inhibitor (paranitrophenol) can now be mixed with the bait
which keeps it in a palatable condition for a reasonable time. In using
this bait it will be essential for a still further extended baiting period
to be planned."

Special liaison is made twice yearly with the Borough Engineer's
department for the treatment of sewers. In 1957 treatments were
carried out in April and September. The method employed in carrying
out this work was to deposit 8 oz. prebait on the first day and if a
complete take was shown, 16 ozs. of prebait were used on the
second day. Where complete takes were shown on the second day, the
poison bait deposited was equal to the prebait. In any case at least 8 ozs.
of poison bait was deposited. Poison takes were not inspected.